It's advertising and brand awareness. Zack & Wiki is great, but only a small percentage of Wii owners will know this or want to take a risk on a game like this, that doesn't describe what it is in the title.

Compare that to Resident Evil, which is more widely known, and you're bound to see a difference.

Forgetting of course that Okami was released on the PS2 two years before the Wii version, and that it sold even LESS on PS2.

Here's an idea ; Try advertising your games if you want people to buy them. At the time Zack & Wiki was released I was a student on a Computer Games Production course. There were other people on the course, some of them huge Nintendo freaks, who had no idea what the game was.